530 



BULLETIN OF THE BUREAU OF FISHERIES 



little or no pigment on the abdominal fins and reduced pigmentation elsewhere, as 

 in the case of the small fish of southern Lake Michigan. The only other small fish 

 (two taken off Marquette, Mich.) are as heavily pigmented as the largest specimens 

 taken from the same locality, so that it is not certain that these small fish from 

 Ontonagon would become darker with age, nor is it certain that all small fish from 

 Marquette would also be dark. 



Pearl organs no doubt are developed by both sexes when spawning,but no spawn- 

 ing fish were collected. It is probable that the descriptions of these excrescences 

 given for Lake Huron specimens will fit those from Superior. 



VARIATIONS 



Racial variations. — Relatively few specimens have been obtained from any 

 locality, as may be seen from Table 87, and the collected specimens indicate that in 

 only one area (Black Bay, a long, rather inclosed bay on the north shore) do the fish 

 seem to have developed any peculiarity of structure that distinguishes them from 

 their relatives in other parts of the lake. The pale fish from Ontonagon are not 

 considered further, as it is not known definitely that pigmentation may not increase 

 with age. The Black Bay whitefish appear to be notably deeper bodied, on the whole, 

 than those from the open lake. The meager data on hand also indicate that the bay 

 fish tend to have fewer lateral-line scales, as in the case of the Lake Erie race, which 

 is also deeper bodied. L/D values for Black Bay specimens and for those from 

 other parts of the lake are compared below: 





3 



3.1 



3.2 



3.3 



3.4 



3.5 



3.6 



3.7 



3.8 



3.9 



i ' 



4.1 



4.2 



4.3 



4.4 



4.5 



4.6 



4.7 



Black Bay __ 



1 



0 



2 



3 



3 



6 



3 



5 



4 



0 



6 



2 



1 

 8 



1 



1 



1 









Lake Superior, _ . 









1 



1 



4 



2 



13 



7 



5 



7 



5 



2 



1 



































The artedi in Black Bay are known also to be deeper bodied (see p. 500), and both 

 the whitefish and the herring show the same general characters that these species 

 exhibit in Lake Erie. It is probable that in each case the peculiar characteristics are 

 a response to the environment. While there are no data to indicate exactly what the 

 environmental conditions are, it is known that Black Bay is conspicuously shallower 

 and warmer than Lake Superior and even than other much smaller but more open 

 bays near it; and it is assumed that Lake Erie, on account of its shallowness and 

 southerly location is the warmest of the Great Lakes. I have no temperature readings 

 for Lake Erie, but records 9 to 25 in Table 13 show the greater warmth of Black Bay 

 as compared with Lake Superior a few miles outside of the bay and with the more 

 open channels and bays of the north shore. Temperature readings for other parts of 

 Lake Superior, given in the same table, all indicate that the main lake is warmed but 

 slowly and that even at the end of the summer its heat budget is not large. In the 

 figures above it is of particular interest to observe that while the surface temperature 

 in Black Bay was not as high on July 20, 1922, as in Simpson Channel, Moffat Strait, 

 or Armour Harbor on August 5 and 10, 1922, yet the temperature at 8 fathoms was 

 from 3.1° to 6.3° warmer than that recorded at only 4 to 5 fathoms below the surface 

 at these points, and at 8 fathoms was 4.4° warmer than the surface water a few miles 

 outside the bay off Thunder Cape Light on the same day. It is noteworthy also in 

 this connection that the whitefish and herring of Lake Winnipeg and certain other 



